diff --git a/js/core/highlight.js b/js/core/highlight.js
index 4d2034769d..fa8c577020 100644
--- a/js/core/highlight.js
+++ b/js/core/highlight.js
@@ -6,15 +6,27 @@ define(
   [
     "core/pubsubhub",
     "core/utils",
-    "deps/highlight",
+    "core/worker",
     "deps/text!core/css/github.css",
   ],
-  function(pubsubhub, utils, hljs, ghCss) {
+  function(pubsubhub, utils, worker, ghCss) {
     // Opportunistically insert the style into the head to reduce FOUC.
     var codeStyle = document.createElement("style");
     codeStyle.textContent = ghCss;
     var swapStyleOwner = utils.makeOwnerSwapper(codeStyle);
     swapStyleOwner(document.head);
+
+    function getLanguageHint(classList) {
+      return Array
+	.from(classList)
+	.filter(function(item) {
+	  return item !== "highlight"
+	})
+	.map(function(item) {
+	  return item.toLowerCase(item)
+	});
+    }
+
     return {
       run: function(conf, doc, cb) {
         // Nothing to do
@@ -26,18 +38,44 @@ define(
           swapStyleOwner(doc.head);
         }
 
-        if (doc.querySelector("highlight")) {
+	if (doc.querySelector(".highlight")) {
           pubsubhub.pub("warn", "pre elements don't need a 'highlight' class anymore.");
         }
 
-        Array
+	const promisesToHighlight = Array
           .from(
             doc.querySelectorAll("pre:not(.idl)")
           )
-          .forEach(function(element) {
-            hljs.highlightBlock(element);
+	  .map(function(element) {
+	    return new Promise(function(resolve, reject) {
+	      const msg = {
+		action: "highlight",
+		code: element.innerHTML,
+		id: Math.random().toString(),
+		languages: getLanguageHint(element.classList),
+	      };
+	      worker.postMessage(msg);
+	      worker.addEventListener("message", function handler(ev) {
+		if (ev.data.id !== msg.id) {
+		  return; // not for us!
+		}
+		worker.removeEventListener("message", handler);
+		element.innerHTML = ev.data.value;
+		resolve();
+	      });
+	      setTimeout(function() {
+		const errMsg = "Timeout error trying to process: " + msg.code;
+		const err = new Error(errMsg);
+		reject(err)
+	      }, 5000);
+	    });
+	  });
+	Promise
+	  .all(promisesToHighlight)
+	  .then(function() { cb() })
+	  .catch(function(err) {
+	    console.error(err);
           });
-        cb();
       }
     };
   }
diff --git a/js/core/worker.js b/js/core/worker.js
new file mode 100644
index 0000000000..24d7589363
--- /dev/null
+++ b/js/core/worker.js
@@ -0,0 +1,4 @@
+"use strict";
+define([], function() {
+  return new Worker("/worker/respec-worker.js");
+});
diff --git a/worker/respec-worker.js b/worker/respec-worker.js
index d9d11a57a1..bcbd509666 100644
--- a/worker/respec-worker.js
+++ b/worker/respec-worker.js
@@ -1 +1,27 @@
-// ReSpec Worker v0
+// ReSpec Worker v0.1.0
+"use strict";
+importScripts("/js/deps/highlight.js");
+
+hljs.configure({
+  tabReplace: "  ", // 2 spaces
+  languages: [
+   "css",
+   "http",
+   "javascript",
+   "json",
+   "markdown",
+   "xml",
+   "xquery",
+  ],
+});
+
+self.addEventListener("message", function(e) {
+  switch (e.data.action) {
+    case "highlight":
+      const code = e.data.code;
+      const langs = e.data.languages.length ? e.data.languages : undefined;
+      const result = self.hljs.highlightAuto(code, langs);
+      const data = Object.assign({}, e.data, result);
+      self.postMessage(data);
+  }
+});